Tool holder assemblies are known that are adapted for use with workpiece feed and machining means or mechanisms for creating a new surface on an object or workpiece, such as a wrench. Such tool holders are used, for example, with workpiece feed and machining mechanisms to change an original rough or irregular edge surface resulting from the method of forming the wrench (e.g. drop forging) into a new, smoothly arced edge surface that is more aesthetically pleasing and easier on the hand of a user of the wrench than the original rough or irregular surface.
One such machining mechanism comprises a belt grinding assembly including a drive mechanism for driving an abrasive belt in a first direction along a path past a backup platen fixed to frame means for the machining mechanism, which platen has a support surface for the abrasive belt adjacent its rear surface that is straight in the direction of travel of the belt and has a uniform shape corresponding to the shape of the edge surface to be radiused in a direction at a right angle to the direction of travel of the belt One such workpiece feed mechanism comprises workpiece or object manipulating means including a wheel for moving the edge surface of the workpiece along an arcuate path about an axis at a right angle to the direction of travel of the belt into forceful engagement with the abrasive coated surface of the belt along the support surface to form the radius on the edge of the workpiece.
FIGS. 1A and 1B illustrate elements of a known tool holder assembly, generally designated by the reference number 1. The workpiece feed means comprises a wheel 2 having slot surfaces 3 defining an opening on the peripheral portion of the wheel 2. The slot surfaces 3 include surfaces defining a dovetail slot which includes bearing surfaces 4 and a bottom surface 5. The known tool holder assembly 1 includes a removable plate (not shown) having shoulder surfaces and a tool receptacle (not shown) projecting radially from the plate. The plate is shaped to be slid into the dovetail slot 3 with the tool receptacle projecting radially therefrom.
The known tool holder assembly 1 also includes four pressure buttons 7 mounted within four generally, cylindrical holes or counterbores 6 which open into the bottom surface 5 of the dovetail slot in the workpiece feed means and four corresponding coil springs 8 mounted between the bottom of the cylindrical hole and a flange on the pressure button 7. The coil springs 8 constantly bias an arcuate top portion 9 of the pressure buttons 7 to project above the bottom surface 5 of the dovetail slot 3. The generally cylindrical holes 6 include lip surfaces 13 opposite the bottom of the hole and adjacent the bottom surface 5 of the dovetail slot 3. The lip surfaces 13 engage the flange on the pressure buttons 7 and restrict the amount of projection of the pressure buttons 7 into the slot 3.
The removable plate includes a bottom surface (not shown) adapted to be engaged with the top portion 9 of the pressure button 7. When the removable plate of the known tool holder is axially slid into the slot 3, the bias of the coil springs 8 biases the arcuate top portion 9 of the pressure button 9 against the bottom surface of the plate and also biases shoulder surfaces (not shown) of the plate toward the bearing surfaces 4 of the dovetail slot 3 and thereby provides a secure frictional engagement between the shoulder surfaces of the plate and the bearing surfaces 4 of the slot 3. The secure frictional engagement between the shoulder surfaces of the plate and the bearing surfaces 4 of the slot 3 is sufficient to hold the tool receptacle means steady as the wheel 2 moves the edge surface of the workpiece along an arcuate path into forceful engagement with the abrasive coated surface of the belt to form the radius on the workpiece Engagement between a side of the plate and a stop surface 47 mounted on the wheel 2 positions the plate at a predetermined location relative to the periphery of the wheel 2.
The known tool holder assembly initially encounters problems when the user slides the plate and attached tool receptacle into the dovetail slot 3. In order to provide sufficient frictional engagement between the bearing surfaces 4 of the slot 3 and the shoulder surfaces of the plate, the coil springs 8 are required to have a relatively high spring constant (i.e. 40 pounds per inch) which may be controlled by a set screw 41. When the user slides the plate and attached tool holder into the slot 3, the user ultimately must overcome the bias of each of the coil springs 8. The bias of the first few coil springs 8 may be overcome relatively easily by manually sliding the plate into the slot 3. However, while the arcuate top portion 9 of the pressure buttons 7 are shaped to afford passage of the plate into the dovetail slot 3, the four coil springs 8 constantly bias the pressure buttons 7 into the bottom of the dovetail slot 3 and against the plate which makes sliding the plate into the slot progressively more difficult as the plate encounters each pressure button 7. The coil springs 8 also bias the shoulder surfaces of the plate into frictional engagement with the bearing surfaces 4 of the dovetail slot 3. Such frictional engagement is difficult to overcome when the plate is slid into the dovetail slot 3, particularly when the user is attempting to slide the plate over the last few pressure buttons 7. This problem is exacerbated by grinding swarf and dirt such as abrasive and metal particles which contaminate the clearances between the pressure buttons 7 and bores 6.
One solution to this problem has been for a user to use an air hammer or like device to fully slide the plate into the dovetail slot 3. This solution, however, causes excessive wear on wear surfaces (i.e. between the arcuate top portion 9 and the bottom of the plate and between the shoulder surfaces of the plate and the bearing surfaces 4 of the slot 3) which further results in undesirable consequences such as wear grooves eroded into the bottom of the plate, loss of frictional engagement between the bearing surfaces and shoulder surfaces of the plate, loss of bias from the coil springs 8, loosening of the tooling, and premature deterioration of the slot surfaces 3. It is believed that the grinding swarf becomes caught between the wear surfaces of the tool holder assembly 1 and "binds the assembly" or acts as an abrasive to accelerate the deterioration of the wear surfaces of the assembly 1.
The known tool holder assembly also encounters problems when the user exchanges the plate and attached tool receptacle with a different plate and attached tool receptacle. For example, the user may desire to exchange the existing tool receptacle (i.e. a tool receptacle for a wrench) with a different tool receptacle (i.e. a tool receptacle for a wrench having a different shape or for a different workpiece altogether such as, for example, a hammer). The coil springs 8 of the known tool holder assembly 1 constantly bias the shoulder surfaces of the plate toward the bearing surfaces 4 of the dovetail slot 3 and thus, constantly provide a secure frictional engagement between the slot 3 and the plate which must be overcome for a plate and tool receptacle to be replaced with a different plate and tool receptacle Again, grinding swarf further exacerbates the problem as it tends to become trapped between wear surfaces such as between the pressure buttons 7 and the bores 6 and between the springs 8 and the pressure buttons. 7 Such an intrusion by the grinding swarf into the clearances of the tool holder assembly 1 results in many undesirable consequences such as preventing the user from sliding the plate completely into the slot 3, premature deterioration of wear surfaces, and jamming of the pressure buttons 7. One solution to this problem entails first blowing the swarf from the slot 3 and then using an air hammer or like device to forcefully slide the plate out of the slot. This solution, however, takes additional time and creates a great deal of wear which, after multiple uses, creates undesirable erosion of the wear surfaces on the plate and slot 3.